This invention relates generally to pumps and pumping methods, and more particularly to wobble plate pumps and pump controls.
Wobble-plate pumps are employed in a number of different applications and operate under well-known principals. In general, wobble-plate pumps typically include pistons that move in a reciprocating manner within corresponding pump chambers. In many cases, the pistons are moved by a cam surface of a wobble plate that is rotated by a motor or other driving device. The reciprocating movement of the pistons pumps fluid from an inlet port to an outlet port of the pump.
In many conventional wobble plate pumps, the pistons of the pump are coupled to a flexible diaphragm that is positioned between the wobble plate and the pump chambers. In such pumps, each one of the pistons is an individual component separate from the diaphragm, requiring numerous components to be manufactured and assembled. A convolute is sometimes employed to connect each piston and the diaphragm so that the pistons can reciprocate and move with respect to the remainder of the diaphragm. Normally, the thickness of each portion of the convolute must be precisely designed for maximum pump efficiency without risking rupture of the diaphragm.
Many conventional pumps (including wobble plate pumps) have an outlet port coupled to an outlet chamber located within the pump and which is in communication with each of the pump chambers. The outlet port is conventionally positioned radially away from the outlet chamber. As the fluid is pumped out of each of the pump chambers sequentially, the fluid enters the outlet chamber and flows along a circular path. However, in order to exit the outlet chamber through the outlet port, the fluid must diverge at a relatively sharp angle from the circular path. When the fluid is forced to diverge from the circular path, the efficiency of the pump is reduced, especially at lower pressures and higher flow rates.
Many conventional pumps include a mechanical pressure switch that shuts off the pump when a certain pressure (i.e., the shut-off pressure) is exceeded. The pressure switch is typically positioned in physical communication with the fluid in the pump. When the pressure of the fluid exceeds the shut-off pressure, the force of the fluid moves the mechanical switch to open the pump""s power circuit. Mechanical pressure switches have several limitations. For example, during the repeated opening and closing of the pump""s power circuit, arcing and scorching often occurs between the contacts of the switch. Due to this arcing and scorching, an oxidation layer forms over the contacts of the switch, and the switch will eventually be unable to close the pump""s power circuit. In addition, most conventional mechanical pressure switches are unable to operate at high frequencies, which results in the pump being completely xe2x80x9conxe2x80x9d or completely xe2x80x9coff.xe2x80x9d The repeated cycling between completely xe2x80x9conxe2x80x9d and completely xe2x80x9coffxe2x80x9d results in louder operation. Moreover, since mechanical switches are either completely xe2x80x9conxe2x80x9d or completely xe2x80x9coff,xe2x80x9d mechanical switches are unable to precisely control the power provided to the pump.
Wobble-plate pumps are often designed to be powered by a battery, such as an automotive battery. In the pump embodiments employing a pressure switch as described above, power from the battery is normally provided to the pump depending upon whether the mechanical pressure switch is open or closed. If the switch is closed, full battery power is provided to the pump. Always providing full battery power to the pump can cause voltage surge problems when the battery is being charged (e.g., when an automotive battery in a recreational vehicle is being charged by another automotive battery in another operating vehicle). Voltage surges that occur while the battery is being charged can damage the components of the pump. Conversely, voltage drop problems can result if the battery cannot be mounted in close proximity to the pump (e.g., when an automotive battery is positioned adjacent to a recreational vehicle""s engine and the pump is mounted in the rear of the recreational vehicle). Also, the voltage level of the battery drops as the battery is drained from use. If the voltage level provided to the pump by the battery becomes too low, the pump may stall at pressures less than the shut-off pressure. Moreover, when the pump stalls at pressures less than the shut-off pressure, current is still being provided to the pump""s motor even through the motor is unable to turn. If the current provided to the pump""s motor becomes too high, the components of the pump""s motor can be damaged.
In light of the problems and limitations described above, a need exists for a pump apparatus and method employing a diaphragm that is easy to manufacture and is reliable (whether having integral pistons or otherwise). A need also exists for a pump having an outlet port that is positioned for improved fluid flow from the pump outlet port. Furthermore, a need further exists for a pump control system designed to better control the power provided to the pump, to provide for quiet operation of the pump, and to prevent voltage surges, voltage drops, and excessive currents from damaging the pump. Each embodiment of the present invention achieves one or more of these results.
Some preferred embodiments of the present invention provide a diaphragm for use with a pump having pistons driving the diaphragm to pump fluid through the pump. The pistons can be integrally formed in a body portion of the diaphragm, thereby resulting in fewer components for the manufacture and assembly of the pump. Also, each of the pistons are preferably coupled (i.e., attached to or integral therewith) to the body portion of the diaphragm by a convolute. Each of the pistons can have a top surface lying generally in a single plane. In some embodiments, each convolute is comprised of more material at its outer perimeter so that the bottom surface of each convolute lies at an angle with respect to the plane of the piston top surfaces. The angled bottom surface of the convolutes allows the pistons a greater range of motion with respect to the outer perimeter of the convolute, and results in reduced diaphragm stresses for longer diaphragm life.
In some preferred embodiments of the present invention, an outlet port of the pump is positioned tangentially with respect to the perimeter of an outlet chamber. The tangential outlet port allows fluid flowing in a circular path within the outlet chamber to continue along the circular path as the fluid exits the outlet chamber. This results in better pump efficiency, especially at lower pressures and higher flow rates.
Some preferred embodiments of the present invention further provide a pump having a non-mechanical pressure sensor coupled to a pump control system. Preferably, the pressure sensor provides a signal representative of the changes in pressure within the pump to a microcontroller within the pump control system. Based upon the sensed pressure, the microcontroller can provide a pulse-width modulation control signal to an output power stage coupled to the pump. The output power stage selectively provides power to the pump based upon the control signal. Preferably, due to the pulse-width modulation control signal, the speed of the pump gradually increases or decreases rather than cycling between completely xe2x80x9conxe2x80x9d and completely xe2x80x9coff,xe2x80x9d resulting in more efficient and quieter operation of the pump.
The pump control system can also include an input power stage designed to be coupled to a battery. The microcontroller is coupled to the input power stage in order to sense the voltage level of the battery. If the battery voltage is above a high threshold (e.g., when the battery is being charged), the microcontroller preferably prevents power from being provided to the pump. If the battery voltage is below a low threshold (e.g., when the voltage available from the battery will allow the pump to stall below the shut-off pressure), the microcontroller preferably also prevents power from being provided to the pump. In some preferred embodiments, the microprocessor only generates a control signal if the sensed battery voltage is less than the high threshold and greater than the low threshold.
Preferably, the pump control system is also capable of adjusting the pump""s shut-off pressure based upon the sensed battery voltage in order to prevent the pump from stalling when the battery is not fully charged. The microprocessor compares the sensed pressure to the adjusted shut-off pressure. If the sensed pressure is less than the adjusted shut-off pressure, the microprocessor generates a high control signal so that the output power stage provides power to the pump. If the sensed pressure is greater than the adjusted shut-off pressure, the microprocessor generates a low control signal so that the output power stage does not provide power to the pump.
In some preferred embodiments, the pump control system is further capable of limiting the current provided to the pump in order to prevent high currents from damaging the pump""s components. The pump control system is capable of adjusting a current limit threshold based upon the sensed pressure of the fluid within the pump. The pump control system can include a current-sensing circuit capable of sensing the current being provided to the pump. If the sensed current is less than the current limit threshold, the microcontroller preferably generates a high control signal so that the output power stage provides power to the pump. If the sensed current is greater than the current limit threshold, the microcontroller preferably generates a low control signal until the sensed current is less than the current limit threshold.
For the method of the invention, the microcontroller preferably senses the voltage level of the battery and determines whether the voltage level is between a high threshold and a low threshold. Preferably, the microcontroller only allows the pump to operate if the voltage level of the battery is between the high threshold and the low threshold. The microprocessor adjusts the shut-off pressure for the pump based on the sensed voltage.
Preferably, the microcontroller can also sense the pressure of the fluid within the pump and can determine whether the pressure is greater than the adjusted shut-off pressure. If the sensed pressure is greater than the shut-off pressure, the microprocessor preferably generates a pulse-width modulation control signal in order to provide less power to the pump. If the sensed pressure is less than the shut-off pressure, the microprocessor preferably determines whether the pump is turned off. If the pump is not turned off, the microprocessor generates a pulse-width modulation control signal in order to provide more power to the pump.
If the sensed pressure is less than the shut-off pressure and the pump is turned off, the microprocessor preferably generates a pulse-width modulation control signal to re-start the pump. The microcontroller senses the pressure of the fluid within the pump and adjusts the current limit threshold based on the sensed pressure. The microcontroller senses the current being provided to the pump. If the sensed current is greater than the current limit threshold, the microcontroller preferably generates a pulse-width modulation control signal in order to provide less power to the pump. If the sensed current is less than the current limit threshold, the microcontroller preferably generates a pulse-width modulation control signal in order to provide more power to the pump.
Further objects and advantages of the present invention, together with the organization and manner of operation thereof, will become apparent from the following detailed description of the invention when taken in conjunction with the accompanying drawings, wherein like elements have like numerals throughout the drawings.